There are many systems and prodcesses for melting glass from glass batch and/or cullet and several systems and ways of increasing melting capacity of tank type melters. For example, It is known to add electrodes through the sides and/or through the bottom of the tank to increase capacity, to preheat batch and to preheat combustion air for improving melting capacity and/or melt quality in tank type glass melters. It is also known to employ oxygen-fuel burners, in a number of various kinds of tank melters to supplement or totally replace the air-fuel burners. The oxygen-fuel burners produce a hotter flame and greater heat transfer than that of air-fuel burners. Oxygen/fuel burners are designed to fire parallel or substantially parallel to the surface of the glass, or are mounted in the crown to direct the flame(s) downward towards the unmelted batch and/or the melt. These burners transfer heat upward into the furnace crown and surrounding refractories as well as into the batch and glass. Heat transfer is achieved by convection, direct radiation from the flame and by re-radiation from the refractory superstructure of the glass furnace. It is also known to preheat the oxygen and/or the gaseous fuel for achieving a hotter flame temperature and faster melting and to move the hot spot closer to the batch end of glass tanks. While these systems and methods have suceeded in increasing melting capacity of the same size tank melters, and in moving the “hot spot” further towards the batch feed end of the tank, the location of the “hot spot” still remains a considerable distance from the optimum desired area that would melt the incoming glass batch faster and better. Also, it is very expensive to enlarge a tank melter, even if the room is available, and even far more expensive to build a new tank melter and all its peripherals, still providing room is available, than to increase the capacity of an existing tank melter and to add on additional forehearth and bushings or other glass forming equipment.
The capacity of the glass tanks are usually limited by the highest temperature of the refractory lining within the melting chamber, particularly on the hot face. Accordingly, one concern in the use of oxygen-fuel burners has been the risk associated with the very high temperature of the burner flames and overheating of the refractory roof and walls of the furnace. It is known from U.S. Pat. Nos. 5,346,524, 6,237,369 and 6,398,547, to provide a refractory lined glass melters for producing refined glass from raw glass-forming material and to use oxy-fuel burner(s) in the tank crown to produce the heat needed to melt glass batch and to refine the resulting molten glass. The oxygen-fuel burner or burners have an inner central cylindrical fuel conduit for providing gaseous fuel and an outer cylindrical oxygen conduit concentric with the central fuel outlet for providing oxygen. The method using such a furnace for producing refined glass from raw glass-forming material in the refractory lined glass melter includes the steps of charging raw glass-forming material to the melting zone of the glass melter. The velocity of the gaseous fuel and the oxygen from the oxygen-fuel burner is controlled such that the velocity of the gaseous fuel and the oxygen are substantially equivalent to provide a generally laminar gaseous fuel flow and generally laminar oxygen flow to combust proximate a top surface of the raw glass-forming material and produce a flame which impinges the surface of the raw glass-forming material and which has a middle portion of an approximately columnar shape. The flame melts the raw glass-forming material within the melting zone by means of the flame coverage from the at least one oxygen-fuel burner without having to use regenerators or recuperators to provide preheated air. Refined molten glass is then withdrawn from the fining zone.
It is also well known to use electric boosting in the air-fuel or oxy-fuel fired furnaces by locating a plurality of electrodes beneath the molten glass to provide a means for adding heat to the molten glass to increase the capacity of the air-fuel or oxy-fuel fired glass tanks. Electric furnaces for melting glass are also well known, but in starting such furnaces the glass batch must initially be melted using combustion burners until sufficient molten glass is produced to cover the electrodes. All electric melters have not proven economical in many instances for processes requiring high tonnage melting rates such as required for products such as E glass continuous fibers, containers such as jars and bottles, tableware and flat glass for windows and display cases. Conventional all electric tank type melters also are not normally used to melt E (electrical) glass for making continuous glass fiber products due to the low electrical conductivity of molten E glass at normal molten glass temperatures.
It is also known from U.S. Pat. No. 6,983,006, to melt and refine glass comprising the steps of: charging glass raw materials into a tank type furnace whose side wall's height is twice or more than twice as long as an inside dimension of a bottom of the furnace so as to thermally melt the glass raw materials; heating molten glass obtained by thermally melting the glass raw materials with heating electrodes that jut from the side wall so as to increase the temperature of the molten glass and that are placed at different levels from the bottom of the surface; charging further glass raw materials into the furnace so as to make a surface level of the molten glass twice or more than twice as high as the lowest level of heating electrodes among the group of electrodes; convecting the molten glass above the heating electrodes while the molten glass is being heated with the heating electrodes; and discharging the molten glass from the bottom of the furnace. Further, in the course of moving down the deep furnace, any air or gas bubbles, seeds, will only go down so far due to their lower density so the seedless molten glass may then be discharged at or near the the bottom of the furnace through an orifice feeder. Such melters are sometimes known as Sorg melters.
More recently it is known to melt glass using burners submerged in the molten glass putting the hot flames of air/gas or oxygen gas, with or without preheat, into the molten glass itself as disclosed in United States patents including U.S. Pat. Nos. 7,428,827, 7,565,819 and 8,561,430. As evidenced by published United States patent applications 2011/0308280 and 2012/0077135, problems have been encountered in submerged burner glass melting, namely severe frequency and/or amounts of molten glass foam, gaseous bubbles and seeds, in the hot molten glass making it difficult, expensive or impractical, to refine for many products.
Most, if not all, of the above described processes and melters were aimed towards improving the capacity of the tank type glass melters and/or to improve the quality of the molten glass and/or to move the “hot spot” closer to the batch entry end of the melter and away from the walls of the melter. However, while these processes and melters have suceeded to varying extents, none have moved the “hot spot” sufficiently to optimize capacity of the existing melters while maintaining desired or acceptable molten glace quality.
Kettle type glass melters, (KTEMs), the E stands for electric, are also known for use in melting glass and even more refractory non-metallic materials as disclosed in U.S. Pat. Nos. 4,017,294 and 4,023,950, 4,143,232, 4,159,392 and 5,643,350, and side discharge melters of this type are disclosed in U.S. patent Nos including U.S. Pat. Nos. 5,961,686, 6,044,667, 6,178,777, 6,314,760 and 6,418,755, 4,017,294, the disclosures of which are hereby incorporated herein by reference. The '294 patent generally describes an open-top electric melter, or furnace, having a central bottom discharge outlet. The melter includes a ceramic lining and a molybdenum outlet member located at the bottom of the melter, at the center thereof. The tapping block of the outlet is made of molybdenum, a material which is able to withstand high temperatures within the furnace and is substantially corrosion resistant. Because the molybdenum tapping block readily oxidizes at the operating temperature, it and the molybdenum exlectrodes that either enter the molten glass through the metal sides of the kettle or through the batch cover on top of the molten gllass must be cooled below their oxidizing temperature and that is done with water cooling as is the metal shell containing the refractory lining and the molten glass. Sometimes a platinum or platinum/rhodium alloy metal is used for an extension of the molybdenum tapping block or orifice and it also is water cooled.
Unfortunately, KTEM glass melters which include outlets located at the bottom center of the melter as disclosed in U.S. Pat. Nos. 3,580,976, 3,659,029, 3,876,817, 3,912,488, 4,017,294, 4,146,375, 4,366,571, 5,573,564, 5,643,350, the disclosures of which are hereby incorporated herein by reference, or even at a side discharge kettle melter as in U.S. Pat. No. 5,961,686, produce glass melt discharge having much higher temperatures than achieved in normal tank type melters, temeratures significantly higher than 2300 or 2400 degrees F. such as above 2425, 2450, 2475, 2500, 2550, 2600, 2650, 2700 or even above about 2,800 or 2,900.degrees to 3,200.degree. F. melt temperatures, higher than is desired for entering a refining section and/or for shaping the glass into the final product, thus requiring coiling in some manner to lower the temperature to that desired, usually below 2,300 degrees F. Accordingly, due to these higher than desired glass temperatures and air bubbles in the hot glass it is necessary to further refine the hot glass before shaping it into a product. One method of apparatus for doing this is a side discharge for the hot glass into a refining chamber as shown in U.S. Pat. No. 5,961,686. In such melters the side-discharge outlet can include an elongated tube comprised of a substantially corrosion resistant metal, and having an entrance end and an exit end thereby to define a molten glass flow communication path between an interior of the melter and a conditioning forehearth.
Kettle melters (KTEM's) of the above types and other types such as stir melters, as shown in U.S. Pat. Nos. 4,143,232, 4,159,392 4,366,571, 5,573,564, 5,643,350 and have been used extensively in the process of melting glass where the production rate is normally substantially less than that produced by conventional glass tanks that can produce at least about 75 tons per day of refined molten glass and usually a much higher rate. Because of their lower melting and refining capacities, lower refractory lining life and the usually higher cost of using all electric melting to melt glass for such uses as making continuous glass fiber, containers, tableware, flat glass and other high tonnage demands, the kettle type melters have not been used to supply large tonnages of molten glass. Another shortcoming of kettle melters for delivering molten glass is that the temperature of the molten glass coming from kettle melters is hundreds of degrees F. higher than desired for glass forming into glass products, thus requiring equipment to cool the molten glass to the desired temperatures, wasting energy and adding to the capital and operating costs. Another problem with the kettle type melters is that one or more of the electrodes, normally molybdenum, the cooling cans protecting the electrodes and needle at the melt line, normally stainless steel, and the orifice outlet, normally a platinum alloy or molybdenum and the melter shell, normally steel or stainless steel, must be cooled to protect against overheating and failing and this is done using water that drains a lot of heat energy away from the melting objective. The discovery of new natural gas and crude oil reserves and technologies to free them up has greatly lowered the cost of natural gas and made gas fired melting tanks the lowest cost for melting glass, thus extending the use of fossile fuel and gas fired tank melters for the forseeable future.
KTEMS of the above types and other types have been used extensively in the process of melting glass where the production rate is normally much less than that produced by conventional glass tanks that can produce at least at least 75 tons per day of refined molten glass and usually much higher rates. Because of their lower melting and refining capacities, lower refractory lining life and the usually higher cost of using all electric melting to melt glass for such uses as making continuous glass fiber, containers, tableware, flat glass and other high tonnage demands, KTEMS have not been used to supply large tonnages of molten glass. An advantage of KTEMS is that they will melt almost any material having a relatively high electrical resistance in the molten state, but the higher the melting point of the material, the higher the temperature of the melt discharge. Another shortcoming of KTEMS for delivering molten glass is that the temperature of the molten glass coming from KTEMS is hundreds of degrees F. higher than desired for glass forming into glass products, thus requiring additional equipment such as air or water cooled pots or long forehearths to cool the molten glass to the desired temperatures, wasting energy and adding to the capital and operating costs. The discovery of new natural gas reserves and technologies to free them up has greatly lowered the cost of natural gas and made gas fired melting tanks desirable for melting glass, thus extending the use of gas fired tank melters for the forseeable future.
Another undesirable feature of electric kettle melters is that the shell, being water cooled, often has to meet boiler standards and regulations. Another problem is the difficulty of heating of a new refractory lining upon startup to avoid severe damage to the refractory lining due to an excessive rate of heating by the molten material. Since the exterior of the refractory lining is against a water cooled shell, it has a temperature of only about 200 degrees F. while the temperature of the molten material on the opposite side of the lining is often well above 2200 degrees F. This large thermal gradient within a sintered or ceramic bonded refractory lining causes severe stresses in the refractory causing cracking and spalling. Also, this large thermal gradient through the lining results in a large and costly heat loss. from the melter causing the electrical efficiency of melting in kettle melters to be substantially lower than in conventional tank type melters.
To reduce refractory spalling problems due to thermal shock or due to steam explosions of cast linings containing water, it is customary to heat the interior of the refractory lining with gas fired burners or electric element panels to dry out the lining and/or to heat up the lining several hundred degrees F. prior to the beginning of the melting process. During this time water must be circulated through the shell to keep it cool enough to avoid steam generation in the cooling system of the shell. This relatively cold shell against the refractory lining causes the lining heat up time to be longer, and when the electric kettle melter is down for lining rebuild, downtime is extremely costly for every hour and minute the melter is not melting the desired material. These disadvantages substantially increase the cost of melting in these types of kettle melters and therefore limit their use in spite of their ease of operation. This disadvantage is becoming more important as the exhausts of fossil fuels used in conventional tank type melters is said to cause environmental problems and objections to increased use is likely to increase even faster in the future, while electric power has the advantage of being produced by nuclear, solar and wind generated electrical power, and other more environmentally desirable sources. Thus, there is a pressing need to further improve and minimize the above described problems with electric kettle type melters.
Much work has been done to replace air-fuel fired glass tanks, with or without recuperators and/or regenerators, with oxy-fuel fired burners, with or without electric boosting using electrical powered submerged electrodes. Because of the relatively long life of such furnaces, usually in excess of 5 years and often several years more than 5 years, these glass tanks often fall short of meeting the need for more capacity to exploit the capacity of the molten glass forming equipment downstream and the need for more product production. Building new glass melting tanks, and the related molten glass forming equipment, such as fiber forming rooms, etc., require large amounts of capital and time, e.g. more than 50-100 million dollars. Projects such as this typically require months of time for preparation and approval and at least a year or more from approval of funds to production. Thus, efforts continue to increase the melting and refining capacity of existing glass melting tanks to be able to reap the large profit potential, reduced capital investment and time savings substantial added capacity can produce.
During the past decade a lot of work to develop the concept of submerged melting using natural gas and oxygen have been evaluated, but foam formation, the difficulty or impossibility of avoiding foam, see U.S. Pat. No. 8,707,739, with the difficulty of addressing the foam problem has greatly limited this technology. Further, much work has been done as evidenced by a substantial number of patent applications filed covering ways to address the foaming problem, but the desire continues to move the “hot spot” further towards the batch feed end of tank melters. Progress has been made, but their still remains substantial need to maximize the melting rate and to improve glass quality and/or efficiency in tank melters and to move the “hot spot” significantly closer to the batch feed end of the tank melters. While oxy-fuel firing has helped greatly, the very hot oxygen-natural gas flames remain above the melt, foam and floating batch limiting the heat penetration needed to move the “hot spot” to the desired location. Submerged burner melting is an attempt to further improve melting, but an undesirable result of foam generation persists. Work continues to find a way to achieve the desired results.
Therefore, there still exists a need for better systems and methods of boosting the capacity and capability of existing tank type glass melters and also for improving the electrical efficiency of kettle type electric melters and all types of HSM melters that use water cooling to cool one or more of electrodes and/or the shell and/or the discharge orifice or outlet.